This application is based on Japanese Patent Application HEI 11-142059, filed on May 21, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to p-type group II-VI compound semiconductor crystals, its growth method, and semiconductor devices made of such crystals.
b) Description of the Related Art
Most of element semiconductors such as Si and Ge and group III-V compound semiconductors such as GaAs can be given n- or p-type conductivity by doping donor or acceptor impurities.
The nature capable of forming semiconductors of both n- and p-types is called bipolar. If group III-V compound semiconductor is used, p- and n-type semiconductors can be formed on the same substrate. By using group III-V compound semiconductor, semiconductor devices having a p-n junction such as light emitting diodes (LED) can be manufactured.
A forbidden bandwidth (bandgap: Eg) is a value specific to crystal.
A light emission wavelength xcex is generally expressed by the following equation.
xcex=1240/Eg
where xcex is a light emission wavelength (nm) and Eg (eV) is a forbidden bandwidth of semiconductor.
The value Eg determines the wavelength of inter-band emission light of crystal, i.e., an emission light color. Of group III-V compound semiconductor, GaAs having a relatively narrow Eg has a forbidden bandwidth Eg of 1.43 eV. The emission light wavelength of GaAs is 870 nm in the infrared range. Of group III-V compound semiconductor, AIP having a relatively broad Eg has a forbidden bandwidth Eg of 2.43 eV. The emission light wavelength of AIP is 510 nm which is green emission.
Most of group II-VI compound semiconductor have Eg larger than that of group II-V compound semiconductor. Therefore, light emission can be expected from blue to royal purple and to a ultraviolet range.
Generally, group II-VI compound semiconductor has high ionicity and is mono-polar. Namely, crystals of group II-VI compound semiconductor have generally only one of n- and p-type conductivities and crystals having both conductivities are rare.
Such mono-polar behavior can be explained by self-compensation.
For example, in group II-VI compound semiconductor crystals ZnS, a void of S negative ion having a smaller size has a smaller coupling energy than that of Zn positive ion having a larger size. The effect that Zn positive ion voids compensate p-type impurities is distinctive, and p-type ZnS is hard to be manufactured. Although the self-compensation effect changes with the type of group II-VI compound semiconductor, the phenomenon that p-type ZnO is hard to be manufactured can also be explained in the manner similar to ZnS. If p-type ZnO crystals can be obtained easily, various semiconductor devices using ZnO can be manufactured.
It is an object of the present invention to provide p-type group II-VI compound semiconductor crystals, more specifically a method of growing p-type ZnO crystals.
It is another object of the present invention to provide p-type group II-VI compound semiconductor crystals, more specifically p-type ZnO crystals and semiconductor devices using such crystals.
In this specification, material containing ZnO as its host element and ZnTe as its dopant or guest element is described simply as ZnO.
According to one aspect of the present invention, there is provided a method of growing p-type group II-VI compound semiconductor crystals, comprising a step of: forming ZnO layers and ZnTe layers alternately on a substrate, the ZnO layer being not doped with impurities and having a predetermined impurity concentration, and the ZnTe layer being doped with p-type impurities N to a predetermined impurity concentration or higher.
According to another aspect of the present invention, there is provided a p-type group II-VI compound semiconductor crystalline material, comprising: a lamination structure of ZnO layers and ZnTe layers alternately stacked on a substrate, wherein N is doped at least in the ZnTe layer.
According to another aspect of the present invention, there is provided a group II-VI compound semiconductor device comprising: a substrate; an n-type group II-VI compound semiconductor layer doped with group III elements and formed on the substrate; and a p-type group II-VI compound semiconductor layer formed on the substrate and having ZnO layers and ZnTe layers alternately laminated, N being doped at least in the ZnTe layer.
As above, p-type ZnO having good crystallinity and small electrical resistance can be grown.